Semiconductor device

ABSTRACT

According to one embodiment, a semiconductor device includes a stacked body, a columnar portion, a first charge storage portion, and a second charge storage portion. The stacked body includes a plurality of electrode layers stacked in a first direction. The plurality of electrode layers includes a first electrode layer, and a second electrode layer. The columnar portion extends in the first direction in the stacked body. The first charge storage portion provides between the first electrode layer and the columnar portion. The second charge storage portion provides between the second electrode layer and the columnar portion. A first thickness in a second direction intersecting the first direction of the first charge storage portion between the first electrode layer and the columnar portion is thicker than a second thickness in the second direction of the second charge storage portion between the second electrode layer and the columnar portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims benefit under 35 U.S.C. § 120 to U.S. application Ser. No. 17/149,029, filed Jan. 14, 2021, which is a continuation of and claims benefit under 35 U.S.C. § 120 to U.S. application Ser. No. 16/707,960, filed Dec. 9, 2019 (now U.S. Pat. No. 10,923,488), which is a continuation of and claims benefit under 35 U.S.C. § 120 to U.S. application Ser. No. 16/049,151, filed Jul. 30, 2018 (now U.S. Pat. No. 10,541,247), which is a continuation of and claims benefit under 35 U.S.C. § 120 to U.S. application Ser. No. 15/460,536, filed Mar. 16, 2017 (now U.S. Pat. No. 10,068,911), which is based upon and claims benefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/376,740, filed on Aug. 18, 2016, the entire contents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device.

BACKGROUND

A semiconductor memory device having a three-dimensional structure has been proposed in which a memory hole is formed in a stacked body including a plurality of electrode layers stacked thereon, a columnar portion is provided in the memory hole, a plurality of charge storage portions are respectively provided between the plurality of electrode layers and the columnar portion in a stacking direction of the stacked body. In order to increase the capacity of the semiconductor memory device, it is desired to increase the number of stacked electrode layers. Increasing the number of stacked electrode layers makes it difficult to form a memory hole having a uniform diameter in the stacking direction. Variations in the diameter of the memory hole in the stacking direction can lead to variations in the coupling ratio between the electrode layer and the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a memory cell array of a semiconductor device of a first embodiment;

FIG. 2 is a schematic sectional view of the memory cell array of the semiconductor device of the first embodiment;

FIG. 3 is a schematic sectional view taken along line III-III in FIG. 2 ;

FIG. 4 is a schematic sectional view taken along line IV-IV in FIG. 2 ;

FIG. 5 is a graph illustrating the relationship between the diameter of the columnar portion and the coupling ratio;

FIGS. 6 to 13 are schematic sectional views showing a manufacturing method of the semiconductor device of the first embodiment;

FIG. 14 is a schematic perspective view of a memory cell array of a semiconductor device of another example of the first embodiment;

FIG. 15 is a schematic sectional view of the memory cell array of the semiconductor device of the first embodiment;

FIGS. 16 to 21 are schematic sectional views showing the manufacturing method of the semiconductor device of the second embodiment;

FIG. 22 is a schematic sectional view of a memory cell array of a semiconductor device of a third embodiment; and

FIGS. 23 to 26 are schematic sectional views showing the manufacturing method of the semiconductor device of the third embodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor device includes a stacked body, a columnar portion, a first charge storage portion, and a second charge storage portion. The stacked body includes a plurality of electrode layers stacked on a substrate in a first direction with an insulator interposed between the electrode layers. The plurality of electrode layers includes a first electrode layer, and a second electrode layer provided between the first electrode layer and the substrate. The columnar portion extends in the first direction in the stacked body. The first charge storage portion provides between the first electrode layer and the columnar portion. The second charge storage portion provides between the second electrode layer and the columnar portion. A first thickness in a second direction intersecting the first direction of the first charge storage portion between the first electrode layer and the columnar portion is thicker than a second thickness in the second direction of the second charge storage portion between the second electrode layer and the columnar portion.

Hereinafter, embodiments will be described with reference to the drawings. The same reference numerals are attached to the same elements in each drawing. The semiconductor device of the embodiment is a semiconductor memory device including a memory cell array.

First Embodiment

Semiconductor Device

FIG. 1 is a schematic perspective view of a memory cell array of a semiconductor device of a first embodiment.

As shown in FIG. 1 , in the semiconductor device of the first embodiment, two directions which are parallel to a major surface 10 a of a substrate 10 and orthogonal to each other are an X-direction and a Y-direction, and a direction which is orthogonal to these X-direction and Y-direction is a Z-direction. For example, the Z-direction corresponds to a first direction, the X-direction corresponds to a second direction, and the Y-direction corresponds to a third direction.

A memory cell array 1 of the semiconductor device of the first embodiment includes a stacked body 100 including a plurality of electrode layers 41, a plurality of columnar portions CL, and a plurality of separating portions ST. The plurality of electrode layers 41 are stacked on the major surface 10 a of the substrate 10 so as to be separated from each other. The number of plurality of stacked electrode layers 41 is arbitrary. For example, each of the plurality of electrode layers 41 includes doped silicon. The doped silicon includes, for example, one or more materials selected from the group consisted of phosphorus, arsenic, and boron.

For example, the higher the impurity concentrations of the plurality of electrode layers 41, the farther from the substrate 10 the electrode layers 41 are. For example, the impurity concentration of the electrode layer 41 closest to the substrate 10 is about 1×10²⁰ cm⁻³, and the impurity concentration of the electrode layer 41 farthest from the substrate 10 is about 3×10²⁰ cm⁻³.

For example, each of the plurality of electrode layers 41 may include metal such as tungsten or molybdenum.

An insulator 40 is disposed among a plurality of electrode layers 41. The insulator 40 may be, for example, an insulating material such as a silicon oxide film, or may be an air gap.

A plurality of electrode layers 41 include a drain-side select gate electrode SGD, a plurality of word lines WL, and a source-side select gate electrode SGS.

For example, the source-side select gate electrode SGS is provided on the substrate 10. For example, the plurality of word lines WL are provided on the source-side select gate electrode SGS. For example, the drain-side select gate electrode SGD is provided on the plurality of word lines WL.

The drain-side select gate electrode SGD functions as a gate electrode of the drain-side select transistor STD. The source-side select gate electrode SGS functions as a gate electrode of the source-side select transistor STS. A plurality of memory cells MC are connected in series between the drain-side select transistor STD and the source-side select transistor STS. One word line WL functions as a gate electrode of one memory cell MC.

The stacked body 100 includes a plurality of separating portions ST. The separating portions ST extend inside the stacked body 100 in the Z-direction and the Y-direction. The separating portion ST separates the stacked body 100 in the X-direction. The region separated by the separating portion ST is called “block”. The block is, for example, a minimum unit of information erase. The erase size is set for one block or a plurality of blocks which are combined.

A source layer SL is provided in the separating portion ST. The source layer SL is insulated from the stacked body 100, and spreads like a plate, for example, in the Z-direction and the Y-direction. An upper layer wiring 80 is provided above the source layer SL. The upper layer wiring 80 extends in the X-direction. The upper layer wiring 80 is electrically connected to a plurality of source layers SL which are arranged in the X-direction.

A plurality of columnar portions CL are provided in the stacked body 100 separated by the separating portion ST. The columnar portions CL extend in the stacked body 100 in the Z-direction.

The columnar portions CL are disposed in the form of, for example, a houndstooth pattern or a square lattice pattern, in the memory cell array 1.

A plurality of bit lines BL are provided above the upper end portion of the columnar portions CL. The plurality of bit lines BL extend in the X-direction. The upper end portion of the columnar portions CL are electrically connected to one of the bit lines BL through the contact portion Cb and the contact portion V1.

FIG. 2 is a schematic sectional view of the memory cell array of the semiconductor device of the first embodiment. FIG. 2 corresponds to a part of the cross section parallel to the XZ plane in FIG. 1 . FIG. 2 is a schematic sectional view obtained by extracting the columnar portion CL and its surrounding portion. FIG. 3 is a schematic sectional view taken along line III-III in FIG. 2 , FIG. 4 is a schematic sectional view taken along line IV-IV in FIG. 2 .

As shown in FIG. 2 , a plurality of electrode layers 41 include, for example, a first electrode layer 41 a, a second electrode layer 41 b, and a third electrode layer 41 c. The second electrode layer 41 b is disposed between the first electrode layer 41 a and the substrate 10. The third electrode layer 41 c is disposed between the first electrode layer 41 a and the second electrode layer 41 b.

As shown in FIGS. 2 to 4 , the columnar portion CL extends in the stacked body 100 in the Z-direction and is electrically connected to the substrate 10. For example, the columnar portion CL has a substantially columnar shape. For example, the columnar portion CL has a tapered shape. In other words, the smaller the diameter of the columnar portion CL, the closer to the substrate 10 the columnar portion CL is.

The columnar portion CL includes a core portion 51 and a semiconductor body 52. The core portion 51 extends in the stacked body 100 in the Z-direction. The semiconductor body 52 is provided between the core portion 51 and the stacked body 100 and between the core portion 51 and the substrate 10.

A plurality of charge storage portions 32 are provided between the columnar portions CL and the plurality of electrode layers 41. For example, the charge storage portions 32 are floating gates or charge trapping layers. An insulator 40 is disposed among the plurality of charge storage portions 32. The respective charge storage portions 32 are spaced apart in the Z-direction by the insulator 40. For example, the smaller the thickness of the charge storage portion 32 between the columnar portion CL and the electrode layer 41, the closer to the substrate 10 the charge storage portion 32 is.

In the specification, the thickness of the charge storage portion 32 is the thickness of the charge storage portion 32 in the direction in the X-direction between the columnar portion CL and the electrode layer 41.

The plurality of charge storage portions 32 include for example, a first charge storage portion 32 a, a second charge storage portion 32 b, and a third charge storage portion 32 c. For example, the first charge storage portion 32 a is disposed between the columnar portion CL and the first electrode layer 41 a. For example, the second charge storage portion 32 b is disposed between the columnar portion CL and the second electrode layer 41 b. For example, the third charge storage portion 32 c is disposed between the columnar portion CL and the third electrode layer 41 c.

For example, the thickness L1 of the first charge storage portion 32 a in the X-direction between the columnar portion CL and the first electrode layer 41 a is thicker than the thickness L2 of the second charge storage portion 32 b in the X-direction between the columnar portion CL and the second electrode layer 41 b.

For example, the thickness L3 of the third charge storage portion 32 c in the X-direction between the columnar portion CL and the third electrode layer 41 c is a thickness not more than the thickness L1. For example, the thickness L3 is a thickness not less than the thickness L2.

A tunnel insulating film 31 is provided between the columnar portion CL and each charge storage portion 32 and between the columnar portion CL and the insulator 40. For example, the tunnel insulating film 31 is cylindrical. For example, the smaller the inner diameter of the tunnel insulating film 31, the closer to the substrate 10 the tunnel insulating film 31 is.

For example, the inner diameter D1 of the tunnel insulating film 31 between the columnar portion CL and the first charge storage portion 32 a is larger than the inner diameter D2 of the tunnel insulating film 31 between the columnar portion CL and the second charge storage portion 32 b.

For example, the size of the inner diameter D3 of the tunnel insulating film 31 between the columnar portion CL and the third charge storage portion 32 c is not more than the size of the inner diameter D1. The size of the inner diameter D3 is not less than the size of the inner diameter D2.

A block insulating film 33 is provided between the charge storage portion 32 and the electrode layer 41. For example, a plurality of block insulating films 33 are provided for respective electrode layers 41.

Examples of the plurality of block insulating films 33 include a first block insulating film 33 a, a second block insulating film 33 b, and a third block insulating film 33 c. The first block insulating film 33 a is disposed between the first charge storage portion 32 a and the first electrode layer 41 a. The second block insulating film 33 b is disposed between the second charge storage portion 32 b and the second electrode layer 41 b. The third block insulating film 33 c is disposed between the third charge storage portion 32 c and the third electrode layer 41 c.

The charge storage portion 32 includes for example, silicon. In a case of a floating gate, the charge storage portion 32 stores charges. In a case of a charge trapping layer, the charge storage portion 32 has a trapping site for trapping charges and traps charges. The threshold of the memory cell MC varies depending on the amount of charge present in the charge storage portion. Thus, the memory cell MC stores information. The tunnel insulating film 31 includes for example, silicon oxide. The tunnel insulating film 31 is a potential barrier between the charge storage portion 32 and the semiconductor body 52. The tunnel insulating film 31 tunnels charges when charges are injected into the charge storage portion 32 from the semiconductor body 52 (write operation), and when charges are diffused from the charge storage portion 32 to the semiconductor body 52 (erase operation). The block insulating film 33 may contain for example, aluminum oxide, may contain silicon oxide, or may be a stacked film thereof. The block insulating film 33 suppresses tunneling from the charge storage portion 32 to the word line during the write operation, and suppresses back tunneling of charges from the word line WL to the charge storage portion 32 during the erase operation.

Assuming that the capacitance of the block insulating film 33 is C_(IPD) and the capacitance of the tunnel insulating film 31 is C_(ox), when the voltage (write voltage) applied to the word line WL during the write operation is V_(PGM), the voltage V_(TNL) applied to the tunnel insulating film during the write operation can be represented by, for example,

V _(TNL)=(C _(IPD)/(C _(IPD) +C _(ox)))×V _(PGM)  (1).

In Equation (1), C_(IPD)/(C_(IPD)+C_(ox)) is called “coupling ratio”.

FIG. 5 is a graph illustrating the relationship between the diameter of the columnar portion and the coupling ratio. FIG. 5 is a graph showing the diameter of the columnar portion CL on the horizontal axis and the coupling ratio on the vertical axis. The solid line shows data when the thickness of each charge storage portion 32 between the columnar portion CL and the electrode layer 41 is 10 nm. The broken line shows data when the thickness of each charge storage portion 32 between the columnar portion CL and the electrode layer 41 is 5 nm.

For example, a configuration in which the columnar portion CL has a tapered shape and the thickness of each charge storage portion 32 between the columnar portion CL and the electrode layer 41 is constant may be considered. In this case, as the diameter of the columnar portion CL decreases, a difference between the inner diameter of the block insulating film 33 and the inner diameter of the tunnel insulating film 31 increases. For example, variations in the difference between the circumferential length of the block insulating film 33 and the circumferential length of the tunnel insulating film 31 are increased between the upper and lower layers of the memory cell array. Therefore, the coupling ratio of the corresponding region changes depending on the diameter of the columnar portion CL. As shown in FIG. 5 , as the diameter of the columnar portion CL decreases, the coupling ratio of the corresponding region increases. For example, a difference ΔC in coupling ratios occurs between a region where the diameter of the columnar portion CL is small and a region where the diameter of the columnar portion CL is large. This results in that variations in the coupling ratio occur between the upper and lower layers of the memory cell array. This results in that variations in the writing speed occur between the upper and lower layers of the memory cell array. During a read operation, read disturb is remarkable.

As shown in FIG. 5 , the coupling ratio in the region where the columnar portion CL is large when the thickness of the charge storage portion 32 is 10 nm shows approximately the same value as the coupling ratio in the region where the columnar portion CL is small when the thickness of the charge storage portion 32 is 5 nm. In the first example, the thickness of the charge storage portion 32 in the region where the diameter of the columnar portion CL is small is shorter than the thickness of the charge storage portion 32 in the region where the diameter of the columnar portion CL is large. With such a configuration, the difference ΔC in coupling ratios between the upper and lower layers of the memory cell can be reduced.

For example, as the diameter of the columnar portion CL decreases, the ratio between the inner diameter of the block insulating film 33 and the inner diameter of the tunnel insulating film 31 is suppressed from increasing. Therefore, the variation in the ratio between the circumferential length of the block insulating film 33 and the circumferential length of the tunnel insulating film 31 is suppressed between the upper and lower layers of the memory cell array. Thus, variations in the coupling ratio between the upper and lower layers of the memory cell array are suppressed. For example, variations in writing speed between the upper and lower layers of the memory cell array can be suppressed. In addition, read disturb and write disturb can be suppressed.

In the first embodiment, in a case where each electrode layer 41 contains doped silicon, the higher the impurity concentration of the electrode layer 41, the farther from the substrate 10 the electrode layer 41 is. Thus, the lower the resistivity of the electrode layer 41, the farther from the substrate 10 the electrode layer 41 is. For example, it is possible to correct the signal propagation delay of the word line caused by the difference in word line resistance, due to a difference between the memory hole diameters of the upper and lower layers of the memory cell array, by controlling the resistivity of the electrode layer 41.

Manufacturing Method

FIGS. 6 to 13 are schematic sectional views showing a manufacturing method of the semiconductor device of the first embodiment. FIGS. 6 to 13 correspond to the cross section shown in FIG. 2 .

As shown in FIG. 6 , the insulator 40 which is a first layer and the electrode layer 41 which is a second layer are alternately stacked on the substrate 10. Thus, the stacked body 100 including the electrode layer 41 stacked on the substrate 10 with the insulator 40 interposed therebetween is formed. The insulator 40 is formed of, for example, a material containing silicon oxide. For example, the electrode layer 41 is formed of a material containing doped silicon. The doped silicon includes, for example, one or more materials selected from the group consisted of phosphorus, arsenic, and boron. For example, the higher the impurity concentration of the electrode layer 41, the farther from the substrate 10 the electrode layer 41 is. For example, the electrode layer 41 may be formed of a material containing metal such as tungsten.

As shown in FIG. 7 , for example, a memory hole MH1 is formed in the stacked body 100 by a photolithography method. The memory hole MH1 extends in the Z-direction in the stacked body 100. The memory hole MH1 penetrates the stacked body 100 and reaches the upper surface of the substrate 10. For example, the memory hole MH1 has a tapered shape. For example, the smaller the diameter of the memory hole MH1, the closer to the substrate 10 the memory hole MH1 is.

As shown in FIG. 8 , a sacrificial member 50 a is formed in the memory hole MH1. For example, the sacrificial member 50 a is formed at the lower part of the memory hole MH1.

As shown in FIG. 9 , an etching process is performed on the end face of the electrode layer 41 exposed in the memory hole MH1. For example, an etchant is supplied into the memory hole MH1. Thus, the end face of the electrode layer 41 exposed in the memory hole MH1 retreats. At this time, the lower part of the memory hole MH1 is filled with the sacrificial member 50 a. Therefore, the electrode layer 41 in the lower part of the memory hole MH1 is not etched.

As shown in FIG. 10 , the sacrificial member 50 a is removed by an etching process such as chemical dry etching or wet etching.

As shown in FIG. 11 , an etching process is performed on the end face of the electrode layer 41 exposed in the memory hole MH1. For example, etchant is supplied into the memory hole MH1. Thus, the end face of the electrode layer 41 exposed in the memory hole MH1 retreats.

By performing the processes shown in FIGS. 9 and 10 , the retreat amount of the end face of the electrode layer 41 increases as the distance from the substrate 10 increases. Note that in the case where the retreat amount of the end face of the electrode layer 41 can be controlled according to the conditions of the etching process or the like, the sacrificial member 50 a may not be formed. For example, when the electrode layer 41 contains silicon and impurity, the etching rate may be controlled by changing the impurity concentration for each electrode layer 41.

Next, as shown in FIG. 11 , the block insulating film 33 is formed on the inner wall of the space generated by the retraction of the electrode layer 41. The block insulating film 33 is formed of, for example, a material containing aluminum oxide. The block insulating film 33 may be formed of a material containing, for example, silicon oxide. Thereafter, the charge storage portion 32 is formed in the space by the retraction of the electrode layer 41. The charge storage portion 32 is formed of a material containing, for example, polysilicon or silicon nitride. Further, the block insulating film 33 and the charge storage portion 32 are etched back by chemical dry etching or the like up to a place where there is no step from the memory hole MH1 and they are aligned with the insulator 40, and are separated for each layer. Thus, the space generated by the retraction of the electrode layer 41 is filled with the block insulating film 33 and the charge storage portion 32.

As shown in FIG. 12 , the tunnel insulating film 31 is formed on the inner wall of the memory hole MH1. The tunnel insulating film 31 is formed of at least one material selected from the group consisted of for example, silicon oxide, silicon oxynitride, and silicon nitride. The tunnel insulating film 31 may be formed as a stacked film including a silicon oxide film, a silicon oxynitride film, and a silicon nitride film.

As shown in FIG. 13 , the semiconductor film 52 a is formed on the tunnel insulating film 31. The tunnel insulating film 31 and the semiconductor film 52 a formed at the bottom of the memory hole MH1 are removed by anisotropic etching. At this time, the tunnel insulating film 31 and the semiconductor film 52 a formed on the side wall of the memory hole MH1 remain. The tunnel insulating film 31 formed on the side wall of the memory hole MH1 is protected from the influence of anisotropic etching by the semiconductor film 52 a formed thereon.

Thereafter, the semiconductor body 52 is formed in the memory hole MH1 as shown in FIG. 2 . The semiconductor body 52 is electrically connected to the substrate 10. The semiconductor film 52 a is a part of the semiconductor body 52. Thereafter, the core portion 51 is formed in the memory hole MH1. The core portion 51 is formed of, for example, a material containing silicon oxide. The memory hole MH1 is filled with the semiconductor body 52 and the core portion 51.

The semiconductor device of the first embodiment can be manufactured by, for example, such a manufacturing method.

In the manufacturing method of the semiconductor device of the first embodiment, the sacrificial member 50 a is formed in the memory hole MH1. Thus, the retreat amount of the end face of the electrode layer 41 is controlled, as shown in FIGS. 8 and 9 .

In the manufacturing method of the semiconductor device of the first embodiment, the impurity concentration may be changed for each electrode layer 41. For example, the farther from the substrate 10, the higher the impurity concentration of the electrode layer 41 may be. Thus, the etching rate of the electrode layer 41 can be controlled. For example, when performing the processes shown in FIGS. 8 and 9 , the etching conditions are relaxed. For example, it is possible to control the retreat amount of the end face of the electrode layer 41 without forming the sacrificial member 50 a.

FIG. 14 is a schematic perspective view of a memory cell array of a semiconductor device of another example of the first embodiment.

Although the memory cell array is formed on the substrate 10 in the above example, a buried source line electrode containing polysilicon or tungsten may be formed flat on a peripheral circuit formed on a silicon substrate, and a memory cell array may be formed on the buried source line electrode.

In this case, a peripheral circuit 11 is provided on the major surface 10 a of the substrate 10 as shown in FIG. 14 . The peripheral circuit 11 includes a transistor Tr provided in the insulating film. A source line electrode 12 (a buried source line electrode) is provided on the peripheral circuit 11. An insulating film 13 is provided on the source line electrode 12. A semiconductor layer 14 is provided on the insulating film 13. The stacked body 100 is provided on the semiconductor layer 14.

Second Embodiment

Semiconductor Device

FIG. 15 is a schematic sectional view of the memory cell array of the semiconductor device of the first embodiment. FIG. 15 corresponds to a part of a cross section parallel to the XZ plane in FIG. 1 . FIG. 15 is a schematic sectional view obtained by extracting the columnar portion CL and its surrounding portion.

As shown in FIG. 15 , a memory cell array 2 of the semiconductor device of the first embodiment includes a stacked body 100, a columnar portion CL, a tunnel insulating film 31, a plurality of charge storage portions 32, and a plurality of block insulating films 33.

The stacked body 100 includes a plurality of electrode layers 41 stacked on a substrate 10 in the Z-direction with an insulator 40 interposed therebetween. The stacked body 100 includes a stacked portion 100 a including a part of the plurality of electrode layers 41 and a stacked portion 100 b including another part of the plurality of electrode layers 41. The stacked portion 100 a is provided on the substrate 10. The stacked portion 100 b is provided between the substrate 10 and the stacked portion 100 a.

The columnar portion CL extends in the stacked body 100 in the Z-direction. The columnar portion CL includes a first columnar portion CLa provided in the stacked portion 100 a and a second columnar portion CLb provided in the stacked portion 100 b.

For example, the first columnar portion CLa and the second columnar portion CLb each have a tapered shape. For example, the smaller the diameter of the first columnar portion CLa, the closer to the substrate 10 the first columnar portion CLa is. The smaller the diameter of the second columnar portion CLb, the closer to the substrate 10 the second columnar portion CLb is. For example, the diameter of the lower end of the first columnar portion CLa is smaller than the diameter of the upper end of the second columnar portion CLb.

The plurality of charge storage portions 32 are provided between the columnar portion CL and the plurality of electrode layers 41. In the stacked portion 100 a, the shorter the thickness of the charge storage portion 32 between the columnar portion CL and one electrode layer 41, the closer to the stacked portion 100 b the charge storage portion 32 is. In the stacked portion 100 b, the smaller the thickness of the charge storage portion 32 between the columnar portion CL and one electrode layer 41, the closer to the substrate 10 the charge storage portion 32 is.

Examples of the plurality of electrode layers 41 include a first electrode layer 41 a, a second electrode layer 41 b, a third electrode layer 41 c, a fourth electrode layer 41 d, a fifth electrode layer 41 e, and a sixth electrode layer 41 f.

The first electrode layer 41 a, the second electrode layer 41 b, and the fifth electrode layer 41 e are included in the stacked portion 100 a. The third electrode layer 41 c, the fourth electrode layer 41 d, and the sixth electrode layer 41 f are included in the stacked portion 100 b.

The second electrode layer 41 b is disposed between the first electrode layer 41 a and the stacked portion 100 b. The fourth electrode layer is disposed between the third electrode layer 41 c and the substrate 10. The fifth electrode layer 41 e is disposed between the first electrode layer 41 a and the third electrode layer 41 c. The sixth electrode layer 41 f is disposed between the third electrode layer 41 c and the fourth electrode layer 41 d.

Examples of the plurality of charge storage portions 32 include a first charge storage portion 32 a, a second charge storage portion 32 b, a third charge storage portion 32 c, a fourth charge storage portion 32 d, a fifth charge storage portion 32 e, and a sixth charge storage portion 32 f.

The first charge storage portion 32 a is disposed between the first columnar portion CLa and the first electrode layer 41 a. The second charge storage portion 32 b is disposed between the first columnar portion CLa and the second electrode layer 41 b. The third charge storage portion 32 c is disposed between the second columnar portion CLb and the third electrode layer 41 c. The fourth charge storage portion 32 d is disposed between the second columnar portion CLb and the fourth electrode layer 41 d. The fifth charge storage portion 32 e is disposed between the first columnar portion CLa and the fifth electrode layer 41 e. The sixth charge storage portion 32 f is disposed between the second columnar portion CLb and the sixth electrode layer 41 f.

The thickness L4 in the X-direction of the first charge storage portion 32 a between the first electrode layer 41 a and the first columnar portion CLa is thicker than the thickness L5 in the X-direction of the second charge storage portion 32 b between the second electrode layer 41 b and the first columnar portion CLa. The thickness L6 in the X-direction of the third charge storage portion 32 c between the third electrode layer 41 c and the second columnar portion CLb is thicker than the thickness L7 in the X-direction of the fourth charge storage portion 32 d between the fourth electrode layer 41 d and the second columnar portion CLb. The thickness L5 is smaller than the thickness L6.

The thickness L8 in the X-direction of the fifth charge storage portion 32 e between the fifth electrode layer 41 e and the first columnar portion CLa is a thickness not more than the thickness L4, and the thickness L8 is a thickness not less than the thickness L5. The thickness L9 in the X-direction of the sixth charge storage portion 32 f between the sixth electrode layer 41 f and the second columnar portion CLb is a thickness not more than the thickness L6, and the thickness L9 is a thickness not less than the thickness L7.

The block insulating film 33 is provided between the electrode layer 41 and the charge storage portion 32. Examples of the plurality of block insulating films 33 include a first block insulating film 33 a, a second block insulating film 33 b, a third block insulating film 33 c, a fourth block insulating film 33 d, a fifth block insulating film 33 e, and a sixth block insulating film 33 f.

The first block insulating film 33 a is disposed between the first charge storage portion 32 a and the first electrode layer 41 a. The second block insulating film 33 b is disposed between the second charge storage portion 32 b and the second electrode layer 41 b. The third block insulating film 33 c is disposed between the third charge storage portion 32 c and the third electrode layer 41 c. The fourth block insulating film 33 d is disposed between the fourth charge storage portion 32 d and the fourth electrode layer 41 d. The fifth block insulating film 33 e is disposed between the fifth charge storage portion 32 e and the fifth electrode layer 41 e. The sixth block insulating film 33 f is disposed between the sixth charge storage portion 32 f and the sixth electrode layer 41 f.

A tunnel insulating film 31 is provided between the columnar portion CL and the charge storage portion 32 and between the columnar portion CL and the insulator 40. For the example, the smaller the inner diameter of the tunnel insulating film 31 between the first columnar portion CLa and the charge storage portion 32, the closer to the stacked portion 100 b the tunnel insulating film 31 is. For example, the smaller the inner diameter of the tunnel insulating film 31 between the second columnar portion CLb and the charge storage portion 32, the closer to the substrate 10 the tunnel insulating film 31 is. The inner diameter of the tunnel insulating film 31 provided around the lower end of the first columnar portion CLa is smaller than the inner diameter of the tunnel insulating film 31 provided around the upper end of the second columnar portion CLb.

For example, the size of the inner diameter D4 of the tunnel insulating film 31 between the first columnar portion CLa and the first charge storage portion 32 a is larger than the size of the inner diameter D5 of the tunnel insulating film 31 between the first columnar portion CLa and the second charge storage portion 32 b. For example, the size of the inner diameter D6 of the tunnel insulating film 31 between the second columnar portion CLb and the third charge storage portion 32 c is larger than the size of the inner diameter D7 of the tunnel insulating film 31 between the second columnar portion CLb and the fourth charge storage portion 32 d. For example, the size of the inner diameter D6 is larger than the size of the inner diameter D5.

For example, the size of the inner diameter D8 of the tunnel insulating film 31 between the first columnar portion CLa and the fifth charge storage portion 32 e is not more than the inner diameter D4. The size of the inner diameter D8 is not less than the size of the inner diameter D5. For example, the size of the inner diameter D9 of the tunnel insulating film 31 between the second columnar portion CLb and the sixth charge storage portion 32 f is not more than the inner diameter D6. The size of the inner diameter D9 is not less than the size of the inner diameter D7.

In the case where the electrode layer 41 contains silicon and impurity, the impurity concentration may vary for each electrode layer 41 in each stacked portion (the stacked portion 100 a and the stacked portion 100 b). For example, in a case where the electrode layer 41 included in the stacked portion 100 a contains silicon and impurity, the higher the impurity concentration, the farther from the stacked portion 100 b the electrode layer 41 is. In the case where the electrode layer 41 included in the stacked portion 100 b contains silicon and impurity, the higher the impurity concentration may be, the farther from the substrate 10 the electrode layer 41 is.

In the semiconductor device of the second embodiment, the smaller the thickness of each charge storage portion 32 between the columnar portion CL and the electrode layer 41, the smaller the diameter of the corresponding tunnel insulating film 31. This prevents the difference between the inner diameter of the block insulating film 33 and the inner diameter of the tunnel insulating film 31 from increasing. Thus, the variations in the coupling ratio are suppressed between the upper and lower layers of the memory cell array. For example, the variations in the write speed can be suppressed between the upper and lower layers of the memory cell array. In addition, it is possible to suppress read disturb and write disturb. This improves the stability of the write operation and the read operation.

In the second embodiment, the impurity concentration of the electrode layer 41 may be changed in the respective stacked portions (the stacked portion 100 a and the stacked portion 100 b). Therefore, the lower the resistivity of the electrode layer 41, the higher the impurity concentration of the electrode layer 41. For example, the larger the diameter of the portion of the tunnel insulating film 31 corresponding to the electrode layer 41, the lower the resistivity may be. For example, it is possible to correct the signal propagation delay of the word line caused by the difference in word line resistance, due to a difference between the memory hole diameters of the upper and lower layers of the memory cell array, by controlling the resistivity of the electrode layer 41.

Manufacturing Method

FIGS. 16 to 21 are schematic sectional views showing the manufacturing method of the semiconductor device of the second embodiment. FIGS. 16 to 21 correspond to the cross section shown in FIG. 14 .

First, the processes shown in FIGS. 6 to 11 are performed in the same manner as in the first embodiment. Thus, the stacked portion 100 b having a memory hole MH1, the charge storage portion 32, and the block insulating film 33 are formed, as shown in FIG. 15 . The stacked portion 100 b corresponds to the stacked body 100 shown in FIG. 11 . A sacrificial member 61 is formed in the memory hole MH1. The memory hole MH1 is filled with the sacrificial member 61.

As shown in FIG. 17 , the insulator 40 which is a third layer and the electrode layer 41 which is a fourth layer are stacked alternately on the stacked portion 100 b. Thereby, the stacked portion 100 a is formed on the stacked portion 100 b.

In the stacked portion 100 b, for example, the electrode layer 41 is formed of a material containing doped silicon. Examples of the doped silicon include one or more materials selected from the group consisted of phosphorus, arsenic, and boron. For example, the higher the impurity concentration of the electrode layer 41 may be, the farther from the stacked portion 100 b the electrode layer 41 is. For example, the electrode layer 41 may be formed of a material containing a metal such as tungsten or molybdenum.

As shown in FIG. 18 , a memory hole MH2 is formed on the sacrificial member 61. The memory hole MH 2 penetrates the stacked portion 100 a in the Z-direction. The upper surface of the sacrificial member 61 is exposed at the bottom of the memory hole MH2.

As shown in FIG. 19 , a sacrificial member 50 b is formed in the memory hole MH2. For example, the sacrificial member 50 b is formed in the lower part of the memory hole MH1. Thereafter, an etching process is performed on the end face of the electrode layer 41 exposed in the memory hole MH2. For example, an etchant is supplied into the memory hole MH2. Thus, the end face of the electrode layer 41 exposed in the memory hole MH2 retreats. At this time, the end portion of the electrode layer 41 in the lower part of the memory hole MH2 is covered with the sacrificial member 50 b. Therefore, the end portion of the electrode layer 41 in the lower part of the memory hole MH2 is not etched.

As shown in FIG. 20 , the sacrificial member 50 b is removed by an etching process such as chemical dry etching. Thereafter, an etching process is performed on the exposed face of the electrode layer 41. For example, an etchant is supplied into the memory hole MH2. Thus, the end face of the electrode layer 41 exposed in the memory hole MH2 retreats.

By performing the processes shown in FIGS. 19 and 20 , the retreat amount of the end face of the electrode layer 41 of the stacked portion 100 a increases as the distance from the stacked portion 100 b increases. Note that in the case where the retreat amount of the end face of the electrode layer 41 can be controlled according to the conditions of the etching process or the like, the sacrificial member 50 b may not be formed. For example, in a case where the electrode layer 41 contains silicon and impurity, the etching rate may be controlled by changing the impurity concentration for each electrode layer 41.

As shown in FIG. 21 , a block insulating film 33 is formed on the inner wall of the space generated by the retraction of the electrode layer 41 of the stacked portion 100 a. The block insulating film 33 is formed of, for example, a material containing aluminum oxide. The block insulating film 33 may be formed of, for example, a material containing silicon oxide. Thereafter, a charge storage portion 32 is formed in the space generated by the retraction of the electrode layer 41 of the stacked portion 100 a. The charge storage portion 32 is formed of, for example, a material containing polysilicon or silicon nitride. Further, the block insulating film 33 and the charge storage portion 32 are etched back by chemical dry etching or the like up to a place where there is no step from the memory holes MH1 and MH2 and they are aligned with the insulator 40, and are separated for each layer. Thus, the block insulating film 33 and the charge storage portion 32 are formed in the stacked portion 100 a. Thereafter, a sacrificial member 50 a is removed by an etching process such as chemical dry etching.

As shown in FIG. 15 , the tunnel insulating film 31 is formed on the side wall of the memory holes MH1 and MH2. A columnar portion CL is formed in the memory holes MH1 and MH2.

The semiconductor device of the second embodiment can be manufactured by for example, such a manufacturing method.

Third Embodiment

Semiconductor Device

FIG. 22 is a schematic sectional view of a memory cell array of a semiconductor device of a third embodiment. FIG. 22 corresponds to a part of the cross section parallel to the XZ plane in FIG. 1 . FIG. 22 is a schematic sectional view obtained by extracting a columnar portion CL and its surrounding portions.

As shown in FIG. 22 , in the memory cell array 3 of the semiconductor device of the third embodiment, a block insulating film 33 is formed between a charge storage portion 32 and an electrode layer 41, and between the electrode layer 41 and an insulator 40. The block insulating film 33 may not be provided between the charge storage portion 32 and the insulator 40. The other configuration is the same as for example, the semiconductor device of the first embodiment. An insulator 70 is provided between the side wall of a separating portion ST and a source layer SL. The insulator 70 contains for example, silicon oxide.

Similar to the first example, the smaller the thickness of each charge storage portion 32 between the columnar portion CL and the electrode layer 41, the closer to the substrate 10 the charge storage portion 32 is. This prevents the difference between the inner diameter of the block insulating film 33 and the inner diameter of a tunnel insulating film 31 from increasing between the upper and lower layers of the memory cell array. This suppresses variations in the coupling ratio between the upper and lower layers of the memory cell array. For example, the variations in the write speed can be suppressed between the upper and lower layers of the memory cell array. In addition, it is possible to suppress read disturb and write disturb. This improves the stability of the write operation and the read operation.

Similar to the first embodiment, in a case where each electrode layer 41 contains doped silicon, the higher the impurity concentration of the electrode layer 41 may be, the farther from the substrate 10 the electrode layer 41 is. Thus, the lower the resistivity of the electrode layer 41, the farther from the substrate 10 the electrode layer 41 is. For example, it is possible to correct the signal propagation delay of the word line caused by the difference in word line resistance, due to a difference between the memory hole diameters of the upper and lower layers of the memory cell array, by controlling the resistivity of the electrode layer 41,

Manufacturing Method

FIGS. 23 to 26 are schematic sectional views showing the manufacturing method of the semiconductor device of the third embodiment. FIGS. 23 to 26 correspond to the cross section shown in FIG. 21 .

First, the processes shown in FIG. 6 are performed. In the third embodiment, the insulator 40 which is a first layer and a replacement member 42 which is a second layer are alternately stacked on the substrate 10. Thereby, a stacked portion 100 is formed on the substrate 10. For example, the small the density of the replacement member 42 may be, the farther from the substrate 10 the replacement member 42 is.

The replacement member 42 is a layer which is later replaced by the electrode layer 41. The material of the replacement member 42 is selected from materials different from the insulator 40, of which the etching selection ratio can be obtained for the insulator 40. For example, when silicon oxide is selected as the insulator 40, silicon nitride is selected for the replacement member 42.

A memory hole MH1 is formed in the stacked body 100 by performing the processes shown in FIG. 7 . After that, the end face of the replacement member 42 exposed in the memory hole MH1 is etched by performing the processes shown in FIGS. 8 to 10 . Thus, the end portion of the replacement member 42 retreats. In a case where the retreat amount of the end face of the replacement member 42 can be controlled according to the conditions of the etching process or the like, formation of the sacrificial member 50 a may be omitted. For example, the etching rate may be controlled by controlling the density of the replacement member 42.

Thereafter, as shown in FIG. 23 , the charge storage portion 32 is formed in the space generated by the retraction of the end portion of the replacement member 42, and the charge storage portion 32 is etched back by chemical dry etching or the like up to a place where there is no step from the memory hole MH1 and it is aligned with the insulator 40, and is separated for each layer.

As shown in FIG. 24 , the tunnel insulating film 31 is formed on the side wall of the memory hole MH1. Thereafter, the columnar portion CL is formed in the memory hole MH1.

As shown in FIG. 25 , the separating portion ST is formed in the stacked body 100. The separating portion ST is formed, for example, by performing anisotropical etching on the stacked body 100. Thereafter, the replacement member 42 is removed. The replacement member 42 is removed, for example, by a wet etching process through the separating portion ST.

As shown in FIG. 26 , the block insulating film 33 is formed on the inner wall of the space generated by removing the replacement member 42. The electrode layer 41 is formed in the space generated by removing the replacement member 42. After that, as shown in FIG. 22 , the insulator 70 is formed on the side wall of the separating portion ST. The source layer SL is formed in the separating portion ST.

The semiconductor device of the third embodiment can be manufactured by, for example, such a manufacturing method.

As described above, according to the embodiment, a semiconductor device capable of suppressing variations in the coupling ratio can be obtained.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. A semiconductor device comprising: a substrate; a first stacked body disposed above the substrate, the first stacked body including a first electrode layer and a second electrode layer, the second electrode layer being disposed above the first electrode layer; a first semiconductor layer extending in a first direction in the first stacked body; a first charge storage portion provided between the first semiconductor layer and the first electrode layer; a second charge storage portion provided between the first semiconductor layer and the second electrode layer; a second stacked body disposed on the first stacked body, the second stacked body including a third electrode layer and a fourth electrode layer, the fourth electrode layer being disposed above the third electrode layer; a second semiconductor layer extending in the first direction in the second stacked body, a bottom end of the second semiconductor layer connecting a top end of the first semiconductor layer; a third charge storage portion provided between the second semiconductor layer and the third electrode layer; and a fourth charge storage portion provided between the second semiconductor layer and the fourth electrode layer, a first diameter of a first portion of the first semiconductor layer being smaller than a second diameter of a second portion of the first semiconductor layer, the first portion being surrounded by the first charge storage portion, and the second portion being surrounded by the second charge storage portion, a third diameter of a third portion of the second semiconductor layer being smaller than a fourth diameter of a fourth portion of the second semiconductor layer, the third portion being surrounded by the third charge storage portion, and the fourth portion being surrounded by the fourth charge storage portion, the second diameter being larger than the third diameter, a first thickness of the first charge storage portion between the first semiconductor layer and the first electrode layer being thinner than a second thickness of the second charge storage portion between the first semiconductor layer and the second electrode layer, and a third thickness of the third charge storage portion between the second semiconductor layer and the third electrode layer being thinner than a fourth thickness of the fourth charge storage portion between the second semiconductor layer and the fourth electrode layer. 